ATLANTA - Democrat Jon Ossoff fought to capture a Republican-held House seat in Atlanta’s wealthy, conservative suburbs Tuesday with a groundswell of grass-roots activism and millions in donations fueled largely by antipathy to President Donald Trump.

Shortly after midnight, unofficial returns showed that Ossoff had fallen below 50 percent of the vote, the threshold needed to declare an outright victory. Instead, Ossoff appeared headed to a runoff against Republican Karen Handel, the top GOP vote-getter in a special election to replace Health and Human Services Secretary Tom Price in Georgia’s 6th Congressional District.

If he is forced into a run-off, Ossoff could find it difficult to sustain the momentum he witnessed this past week in a traditionally Republican district that has been in GOP hands since 1979. Although Handel had earned less 20 percent of the vote with 86 percent of precincts reporting, in a runoff she was widely expected to rally Republican voters who had divided their votes among 11 GOP candidates Tuesday.

Just before midnight, at her election night party in Roswell, Handel thanked supporters and urged Republicans to unite. “Tomorrow we start the campaign anew,” she said.

Ossoff took the stage at his own party, his voice hoarse. “I know it has been a long evening and it looks like it may be a longer one. We may not know the outcome for some time.” But, he added to the roaring crowd holding signs, “there is no doubt this already a victory for the ages.”

“We will be ready to fight on and win in June if it’s necessary,” Ossoff said. “Bring it on.”

Handel’s showing was due to more than name recognition from her long tenure in state politics. She also benefited from $1.3 million in support from Ending Spending, a conservative advocacy group aligned with the billionaire Ricketts family.

National GOP groups, meanwhile, are readying new waves of television advertising.

Democrats had hoped to upend the national political landscape with a stunning victory in this round of voting, rousing their demoralized party just five months after Trump won the White House and stoking a burgeoning anti-Trump movement across the country. Ahead of next year’s mid-term elections, they saw an opportunity to raise expectations about possibly winning back majorities in Congress.

Ossoff’s candidacy gave Democrats an exhilarating if brief taste of what it will be like to compete in a ruby-red district next year, when they have to win 24 seats to take back the House.

Republicans, at war with each other as much as with Democrats, were hoping to escape with a reprieve in the turbulent age of Trump. Facing more battles to come in 2018, the contest gave them little clarity about the party’s ideological drift and how much it should be tethered to the president in the future.

Many Democrats moved quickly to frame the energy around Ossoff’s bid as a damaging referendum on Trump as he nears the 100-day mark of a presidency so far defined by an early stumble on health-care legislation and a GOP split into bickering factions.

Even as the campaigns waited for the count to finish, Ossoff’s team cast the incomplete results in a glowing light.

“While we await the final election results this evening, our first-place finish is a remarkable achievement that many said would never even happen,” said Ossoff campaign manager Keenan Pontoni. “It’s clear that Jon has incredible energy and support behind him that will only grow whether we win tonight or in June.”

Per Georgia law, a run-off ballot would feature the two top finishers from the crowded non-partisan primary, which was called after Republican Tom Price, who had represented the district since 2005, vacated the seat to become Trump’s secretary of health and human Services. The district is a bastion of white college-educated professionals and upscale shopping centers.

Ossoff, 30, a former congressional staffer and political novice who catapulted to national notice, raised more than $8 million and drew heavy support from prominent Democrats and liberal organizers. They saw his campaign, as well as a special House election last week in Kansas where a Democrat narrowly lost, as symbolic battlegrounds for their recovering party.

Trump personally intervened in the final days, which risked becoming a political squall. On Tuesday, he tweeted that Republicans “must get out today and VOTE in Georgia 6” and warned that “Dem Ossoff will raise your taxes” and is “very bad on crime.”

White House officials, such as chief strategist Stephen Bannon, paid close attention to the Georgia election, well aware of the implications for Trump’s political capital as the president attempts to jolt his agenda in the coming months.

Trump continued to weigh in on the race in the late afternoon, pointing out in a tweet that Ossoff “doesn’t even live in the district.” Republicans, he implored at 4:38 p.m. Eastern, “get out and vote!”

Ossoff acknowledged in a CNN interview that he lives with his girlfriend near Emory University, which is outside of the district.

“I’ve been living with my girlfriend, Alicia, for 12 years now down by Emory University where she’s a full-time medical student,” Ossoff said. “As soon as she concludes her medical training, I’ll be 10 minutes back up the street in the district where I grew up.”

CNN’s Alisyn Camerota, intrigued, then asked, “So when are you going to marry her?”

“Well, I don’t want to give anything away,” Ossoff said. “I’ll give you a call when I have something to announce.”

The clip was quickly picked up by news outlets. Looking ahead to a likely run-off, national Republicans seized on Ossoff’s statement as another example of his lack of roots in the district, a critique that has been made repeatedly against the Democrat throughout the campaign. The Drudge Report, a driver of conservative web traffic, made the story its banner, knocking the “Dem Trump slayer” as an interloper.

When asked Tuesday on Air Force One whether the Georgia race was a referendum on Trump’s first 100 days, White House spokesperson Sarah Huckabee Sanders said, “I wouldn’t use the word referendum.”

“I think [Trump] hopes to have a Republican elected to that seat, and hopefully it will be someone to follow in Tom Price’s footsteps and be a leader from that district,” Sanders told reporters.

At Ossoff’s cramped phone bank in Chamblee, situated between dental offices and piled with doughnut boxes and campaign posters, his staffers joked that the tweets amounted to an in-kind contribution that would incite their party’s base to show up. Trump’s messages also reflected how this once sleepy race had landed at the center of the political universe.

“The campaign has taken on a life of its own,” said Ossoff aide Alyssa Castillo, 20, who works in public relations for a distribution center in DeKalb County. “Whatever happens, this is the start of something bigger, that’s for sure.”

Celia Henson, a stay-at-home mother from Decatur who identifies as an independent Democrat, said Tuesday night that Trump retains his support “from most people around here who like him since nothing he does seems to get him in trouble.”

But more on-the-fence voters in the Atlanta suburbs, Henson said, have grown restless or uneasy about the president since his inauguration in January and since he has “kept tweeting.”

“This is a district where people care about respect, people being respected and they don’t like how he acts,” she said.

In the final, frantic hours of canvassing and phone calls, avoiding a runoff was the priority. “No run-off, vote for Ossoff,” read one poster at the Chamblee office.

“Look at the map,” Tish Naghise, an Ossoff field organizer, said as she pointed to a green layout of the district on the wall. “Hillary Clinton came close to winning here, but you have to do really well in Chamblee and Tucker, do well in diverse areas, if you’re going to have a shot of competing throughout this whole area.”

The Republican slate in the 6th District had been roiled in recent weeks by nerves about Trump and lingering internecine dramas over ideological purity and local loyalties. While some GOP candidates sought to align closely with Trump, others chose more cautious paths in an effort to navigate the president’s mixed popularity here.

Trump has become a complicated figure in establishment Republican enclaves such as Chamblee, where Ossoff’s navy-blue campaign signs have sprung up along sidewalks and in apartment windows.

Republicans’ failure to pass their plan to overhaul the nation’s health-care system frustrated some suburban GOP voters about Trump’s effectiveness in cutting deals with lawmakers in Washington, as well as about the party’s promises.

The National Republican Congressional Committee dispatched staffers to Georgia to boost turnout among core GOP voters amid those grumbles. The Congressional Leadership Fund, an outfit aligned with the House GOP, has spent more than $2 million on a spate of negative television spots about Ossoff.

Several GOP candidates - Dan Moody, Bob Gray, Bruce LeVell, Amy Kremer - embraced Trump and cast themselves as his would-be allies in Washington. Others were supportive but not always enthusiastic, such as Handel and Hill. One Republican, David Abroms, opposed the president. Most of the leading candidates bounced between those poles depending on the day or the latest controversy.

Voters veered between wanting a typical Republican to preferring a Trump-style hard-liner.Some tried to sidestep questions about loyalty to Trump, and the varying levels of support the president has seen from Republican candidates here in the 6th.

“We didn’t support Karen based on who she supported for President,” says Allison Newman, a 42 year-old special education teacher, when asked why she and her husband supported Handel, “We supported Karen based on her track record, she’s ethical and she’s a good person.”

Others embraced the president. “It’s important that he agrees with Trump on issues of trade and certain platforms of Trump’s campaign,” said Brendan Foy, 36, a volunteer for Gray who also served as a North Carolina field director last year for Trump. “I voted for him the same reasons Michigan, Wisconsin, and Pennsylvania voted for him.”

LeVell, an African American jeweler and former Trump campaign adviser, as well as Trump-aligned conservative activist Kremer, never gained traction in a Republican district that is not dominated by grass-roots nationalism. Abroms, who campaigned with anti-Trump independent Evan McMullin, also failed to land on the political map.

Gray was seen by Republicans in recent days as having the best shot of outpacing Handel and making a runoff, since he began inching up in various eleventh-hour polls.

At Gray’s campaign office in Johns Creek on Tuesday, his effort to tie himself to Trump was obvious. A massive poster of Vice President Mike Pence greeted visitors at the office entrance. To the right, a yard sign from the Trump campaign was propped against a stack of “Gray for Congress” signs. In a conference room, a photo of the president gave a big thumbs-up to phone-banking volunteers.

Brittany Evrard, 27, a volunteer for the Gray campaign, said Gray’s pro-Trump stance was “very much” part of what made up her mind.